ddRAD-seq based phylogeographic study of Sargassum thunbergii (Phaeophyceae, Heterokonta) around Japanese coast.

Using genome-wide SNP data obtained from high-throughput techniques based on double digest restriction site-associated DNA sequencing (ddRAD-seq), we elucidated the migration history and genetic diversity of the Japanese population of the ecologically important brown seaweed Sargassum thunbergii (Mertens ex Roth) Kuntze. STRUCTURE and NeighborNet analyses showed a clear genetic differentiation among populations of four geographic regions: Kyushu (POP1); Sea of Japan (POP2); Hokkaido and Tohoku (POP3); and Pacific coast from Kyushu to Kanto (POP4). Approximate Bayesian Computation (ABC) analysis indicated that POP4 diverged first, followed by the separation between POP2 (the largest effective population size) and POP3; POP1 was the last to form, shaped by the mixture of POP2 (73%) and POP4 (27%).